Light pipe illumination system and method

ABSTRACT

A system and method is provided for illuminating a subject using a light pipe that transmits light from a source, such as an LED ring illuminator to an outlet that directs the light appropriately as either bright field illumination, dark field illumination or both. The light pipe can include concentric cylinders, typically with a bright field illuminator nested within a dark field illuminator. The tip of the dark field illuminator may be angled so as to internally reflect light inwardly toward the central optical axis of a camera at a low angle. The tip can be located near the focal plane of the camera for the desired field of view. The field of view of the camera sensor can be modified to reject data outside of a illumination field of a particular shape. This illumination field can be created by shaping the light pipe in a predetermined form that projects the modified illumination field. Likewise, a set of aiming illuminators (in, for example, a noticeable color) can be provided around the perimeter of the light pipe to delineate outer boundaries of the illumination field or area of interest. These approaches facilitate better aiming of the sensor into the desired area of interest so that it is illuminated and/or acquired most-fully.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/693,626, filed on Oct. 24, 2003, and entitled “Light PipeIllumination System and Method,” which is hereby incorporated byreference.

FIELD OF THE INVENTION

This invention relates to illuminators and more particularly toilluminators for image acquisition devices and machine vision systems.

BACKGROUND OF THE INVENTION

Machine vision systems use image acquisition devices that include camerasensors to deliver information on a viewed subject. The system theninterprets this information according to a variety of algorithms toperform a programmed decision-making and/or identification function. Foran image to be most-effectively acquired by a sensor in the visible, andnear-visible light range, the subject should be properly illuminated.

In the example of barcode scanning using an image sensor, good lightingis highly desirable. Barcode scanning entails the aiming of an imageacquisition sensor (CMOS camera, CCD, etc.) at a location on an objectthat contains a bar code, and retrieval of an image of that barcode. Thebar code contains a set of predetermined patterns that represent anordered group of characters or symbols from which an attached dataprocessor (for example a microcomputer) can derive useful informationabout the object (e.g., its serial number, type, model, price, etc.).Barcodes are available in a variety of shapes and sizes. Two of the mostcommonly employed barcode types are the so-called one-dimensionalbarcode, consisting a line of vertical stripes of varying width andspacing, and the so-called two-dimensional barcode consisting of atwo-dimensional array of dots or rectangles.

In reading barcodes or other subjects of interest the type ofillumination employed is of concern. Where barcodes and other viewedsubjects are printed on a flat surface with contrasting ink or paint, adiffuse, high-angle “bright field” illumination may best highlight thesefeatures for the sensor. By high-angle it is meant, generally, lightthat strikes the subject nearly perpendicularly (normal) or at an anglethat is typically no less than about 45 degrees from perpendicular(normal) to the surface of the item being scanned. Such illumination issubject to substantial reflection back toward the sensor. By way ofexample, barcodes and other subjects requiring mainly bright fieldillumination may be present on a printed label adhered to an item orcontainer, or on a printed field in a relatively smooth area of item orcontainer.

Conversely, where a barcode or other subject is formed on amore-irregular surface or is created by etching or peening a patterndirectly on the surface, the use of highly reflective bright fieldillumination may be inappropriate. A peened/etched surface hastwo-dimensional properties that tend to scatter bright fieldillumination, thereby obscuring the acquired image. Where a viewedsubject has such decidedly two-dimensional surface texture, it is bestilluminated with dark field illumination. This is an illumination with acharacteristic low angle (approximately 45 degrees or less, for example)with respect to the surface of the subject (i.e. an angle of more thanapproximately 45 degrees with respect to normal). Using such low-angle,dark field illumination, two-dimensional surface texture is contrastedmore effectively (with indents appearing as bright spots and thesurroundings as shadow) for better image acquisition.

To take full advantage of the versatility of a camera image sensor, itis desirable to provide both bright field and dark field illuminationfor selective or simultaneous illumination of a subject. However, darkfield illumination must be presented close to a subject to attain thelow incidence angle thereto. Conversely, bright field illumination isbetter produced at a relative distance to ensure full area illumination.

In addition, a current-production sensor may have a resolution of640×480 (over 300 K) or 1280×1024 (over 1.3 M) pixels within its nativefield of view. This resolution is desirable for attaining an accurateimage of the subject. However, processing speed may be compromised bythe need to acquire every pixel in the field of view even if the subjectis a relatively small part of that field (for example, the narrow stripof a one-dimensional barcode). If the field of view is to be narrowed toonly encompass an area of interest, then a system for aiming the cameraonto that area of interest is desirable. Likewise, where a given fieldof view may contain multiple codes or subjects, the ability to focusupon particular parts of that field of view to discern the selectedsubject is also desirable.

SUMMARY OF THE INVENTION

This invention overcomes the disadvantages of the prior art by providinga system and method for illuminating a subject using a light pipe thattransmits light from a source, such as an LED ring illuminator to anoutlet that directs the light appropriately as either bright fieldillumination, dark field illumination or both. The light pipe caninclude concentric or coaxial (nested) cylinders, typically with abright field illuminator nested within a dark field illuminator. The tipof the dark field illuminator is angled so as to internally reflectlight inwardly toward the central optical axis of a camera at a lowangle. The tip can be located near the focal plane of the camera for thedesired field of view. The field of view of the camera sensor can bemodified to reject data outside of a illumination field of a particularshape. This illumination field can be created by shaping the light pipein a predetermined form that projects the modified illumination field.Likewise, a set of aiming illuminators (in, for example, a noticeablecolor) can be provided around the perimeter of the light pipe todelineate outer boundaries of the illumination field or area ofinterest. These approaches facilitate better aiming of the sensor intothe desired area of interest so that it is illuminated and/or acquiredmost-fully.

According to various embodiments herein, a dark field illuminator,bright field illuminator or combination of dark field and bright fieldilluminator can be provided using an appropriate light pipe or nestedlight pipes. A camera sensor is provided within the interior of thelight pipe arrangement with appropriate optics to view the subjectthrough a channel formed by the innermost wall of the light-pipearrangement. In one embodiment, the dark field illuminator light element(for example, a ring of light sources/LEDs) can be divided into segmentsso that the pattern of light can be modulated relative to thecircumference of the illuminator.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention description below refers to the accompanying drawings, ofwhich:

FIG. 1 is a perspective view of a handheld scanning system and subjectemploying a light pipe illuminator according to an embodiment of thisinvention;

FIG. 2 is a perspective view of a fixedly mounted scanning system andsubject employing a light pipe illuminator according to an embodiment ofthis invention;

FIG. 3 is a schematic cross section of a light pipe and ring illuminatoraccording to an embodiment of this invention;

FIG. 4 is a side cross section of a sensor with dark field illuminatinglight pipe according to an embodiment of this invention;

FIG. 5 is a side cross section of a sensor with bright fieldilluminating light pipe and aiming illuminators according to anembodiment of this invention;

FIG. 6 is a plan view of a circular illumination pattern projected bythe illuminating light pipe of FIG. 5;

FIG. 7 is a plan view of a rectangular/square illumination patternprojected by the illuminating light pipe of FIG. 5, encompassing thesensor's full field of view;

FIG. 8 is a side cross section of a sensor with bright fieldilluminating light pipe, nested within a dark field illuminating lightpipe and aiming illuminators according to an embodiment of thisinvention;

FIG. 9 is a perspective view of a handheld scanning system employing alight pipe that illuminates a modified or restricted sensor field ofview according to an alternate embodiment;

FIG. 10 is a plan view of a rectangular illumination pattern projectedby the illuminating light pipe of FIG. 9, encompassing amodified/restricted sensor field of view; and

FIG. 11 is a side cross section of the sensor and light pipe illuminatorthat can be used to generate a predetermined bright field pattern suchas, for example that of FIG. 9.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

FIG. 1 shows a scanning system 100 adapted for handheld operation. Anexemplary handheld scanning appliance or handpiece 102 is provided. Itincludes a grip section 104 and a body section 106. The sensor and otherfunctional components described herein can be controlled and can directimage data to an on-board/embedded processor 109. This processor caninclude a scanning software application 113 by which lighting iscontrolled, images are acquired and image data is interpreted intousable information (for example, alphanumeric strings derived from thebarcode images). The decoded information can be directed via a cable 110to a PC or other data storage device 112 having (for example) a display114, keyboard 116 and mouse 118, where it can be stored and furthermanipulated using an appropriate application 120. Alternatively, thecable 110 can be directly connected to an interface in the scanningappliance and an appropriate interface in the computer 112. In this casethe computer-based application 120 performs various image interpretationand lighting control functions as needed. The precise arrangement of thehandheld scanning appliance with respect to an embedded processor,computer or other processor is highly variable. For example, a wirelessinterconnect can be provided in which no cable 110 is present. Likewise,the depicted microcomputer can be substituted with another processingdevice, including an onboard processor or a miniaturized processing unitsuch as a personal digital assistant or other small-scale computingdevice.

The scanning application 113 can be adapted to respond to inputs fromthe scanning appliance 102. For example, when the operator toggles atrigger 122 on the appliance 102, an internal camera image sensor (150,shown and described further below) acquires an image of a region ofinterest 130 on an item 132. The exemplary region of interest includes atwo-dimensional bar code 134 that can be used to identify the part 132.Identification and other processing functions are carried out by thescanning application 113, based upon image data transmitted from theappliance 102 to the processor 109.

Simultaneously with, or in advance of acquisition of the image, the areaof interest 130 is illuminated. In one embodiment, a switch 140 on theappliance 102 can be used to operate the illuminator, which consists ofa novel light pipe arrangement 142 in accordance with this invention.Alternatively, as will be described below, the operation of theilluminator can be operated and controlled remotely by the scanningsoftware application 120. The light pipe 142 consists of an extendedbarrel of light transmissive material terminating (in this embodiment)in an angled tip 144. As described further below, this tip is designedto cause internal reflection that projects a low-angle dark fieldillumination in the area of interest 130. As noted above, such darkfield illumination is typically provided at an angle of no more thanapproximately 45 degrees with respect to the surface or more than 45degrees normal to the optical axis. Extending through the center of thelight pipe, which comprises a hollow tube, is a camera sensor 150 (shownin phantom and associated optics). The focal point of the camera isselected so that it is able to focus on the desired area of interest, asits field of view, in close proximity to the tip 144. In this manner,the tip can be placed very close to, or in contact with the area ofinterest for accurate viewing. As noted above, the bar code 134 in thisembodiment is one that is best viewed using a dark field illumination.However, as will be described further below, the light pipes describedin accordance with this invention also has the ability to provide brightfield illumination for bar codes that are better suited to direct,high-angle illumination (for example, those printed with high contrastink on a relatively smooth, matte surface).

FIG. 2 shows another implementation of the light pipe in accordance withan embodiment of this invention. An embedded processor 109 and/orcomputer 112 and associated applications 113 and/or 120 similar to thosedescribed above can be employed. An associated cable 210 interconnectsthe computer, via an interface, with a camera element 220. The cameraelement can be a conventional camera mounted on a fixed bracket 222. Itincludes a lens and electro-optical sensor assembly 224 (shown inphantom). The light pipe is removably mounted via a securing ring 226with exemplary securing screws 228 in this embodiment. Note, whilescrews 228 are use, any fastener system can be substituted. A cable 230,shown in phantom, interconnects an internal ring illuminator, integralwith light pipe, to either the processor 109 or the computer 112. Thisarrangement allows the light pipes of this invention to be secured as aretrofit to a variety of preexisting cameras. In any of the embodimentsherein, the illuminator can be integrated with the camera's standardoperating functions, such as its strobe and trigger mechanisms, or itcan be controlled via the scanning application. Separate controlcircuitry can also be provided to modulate certain functions of theilluminator as described further below. In the example of FIG. 2, theilluminator is viewing parts or other items 216 moving along a conveyer262. The area of interest 264 is a bar code that is best viewed using,for example, bright field illumination. As described below, the lightpipe arrangement, in accordance with the various embodiments of thisinvention, can accommodate bright field illumination as well as darkfield illumination. In both FIGS. 1 and 2, and other figures describedherein, the image sensor is, typically, a commercially available CMOS orCCD image sensor with a resolution of, for example, 640×480 pixels or1280×1024 pixels. Other resolutions and sensor types are expresslycontemplated, however.

With reference to FIG. 3, a version of the light pipe 310 described inFIGS. 1 and 2 is shown. This light pipe includes an outer tube 312 and anested, inner tube 314. The innermost wall of the inner tube 314defines, in this example, a circular lumen or channel. This channel is apath through which light can pass from the area of interest 320 to aboard-mounted or separately placed sensor 330. The lumen has a diameterWL that is equal to or greater than the diameter of the optics of thecamera sensor. In this embodiment, note that the sensor is mounted on acircuit board 332 that also includes the ring illuminator 334. This ringilluminator consists of an outer ring of LEDs or other appropriate lightsources 336 and an inner ring 338 of LEDs or other appropriate lightsources. The number of light sources, size of the rings and their shapeare highly variable. Thus, the term “ring” should be taken broadly todescribe a variety of regular and irregular curved (ovular, etc.) and/orpolygonal (rectangular, square, etc.) perimeter shapes. In general, thering illuminator's light sources are placed relatively close to theouter perimeter of the sensor and/or its optics and the number ofsources is sufficient to fill in the illumination field and supplyappropriate light to the subject. In general, any group of light sourcesor one or more continuous sources (e.g., tubes) arranged to light aperimeter of any size/shape can be broadly considered to be a “ring”light source herein. In one embodiment, the ring can define a circlethat is approximately 3-4 inches in outer diameter. Each ring is alignedwith respect to one of the light pipes 312 and 314. As described below,appropriate baffles separate the rings from each other so that lightfrom one ring does not leak into the other ring.

As noted, each light pipe is constructed from a light-transmissivematerial. This material can be acrylic, glass, or any other materialcapable of acting as a wave guide for visible and near-visible light.The wall thickness of each pipe may vary. In general, thicknesses arebetween approximately ⅛ inch and ¼ inch. However, larger or smallerthicknesses are expressly contemplated. The overall length of the outerlight pipe is also highly variable. As noted above, it is set so thatthe focus on the desired field of view is attained near, but beyond, theend of the tip 340. In one embodiment, the outer light pipe has a lengthof approximately 3-4 inches. The inner light pipe 314 can beapproximately the same length as the outer light pipe, but in thisembodiment, the inner light pipe is recessed with respect to the outer,as shown, so that light can exit from the inner edge of the tip 340. Thetip's light-transmissive region is shown by the dashed line 342. Thisinner-edge light outlet can be formed by exposing and/or polishing astrip in the otherwise opaque overall surface of the outer light pipe312. This light transmissive strip or region can extend (for example) ¼inch, more or less, as shown by thickness T. The thickness T isvariable. Due to internal reflection caused by the angled portion 350 ofthe tip 340, low angle illumination 352 exits from the open region 342.Similarly, the open tip 360 of the inner light pipe 314 facilitatesdirect, bright field illumination 362 on the area of interest 320. Themechanics of the nested light pipe 310 are described in further detailbelow. Reference will first be made to FIG. 4, which describes, moreparticularly, a dark field illuminator. Reference will also be madegenerally to the ring illuminator 334 and controller 370 of FIG. 3.

Note that, while an opaque coating of paint or another acceptablematerial is used to insulate the dark field light pipe against lightleakage, it is contemplated that all or a portion of the light pipe canremain uncovered, particularly where the surface is sufficientlywell-polished to cause near-total internal reflection along its length.

As shown in FIG. 4, a single ring illuminator of LEDs or other lightsources 410 may be provided on a circuit board 412 along with a CMOS,CCD or other electro-optical sensor 414. Note that the sensor, asdescribed in any of the embodiments herein, may be separate from thelight source's circuit board or combined with it. These elementsinterconnect to a controller and/or image acquisition processor similarto those shown in FIG. 3. A dark field-illuminating light pipe 420 isshown in cross-section. This surrounds the image sensor 414 and itsassociated optics 422. A transparent window 424 can be provided in frontof the optics 422 to protect the circuitry. As noted above, the tip 430of the light pipe 420 is angled at an angle A (approximately 45 degreesor more) so that light is reflected to pass through an exposed thicknessT along the inner perimeter of the light pipe using internal reflection.The light transmits with the desired low-angle (or a high-angle (over 45degrees) respect to optical axis centerline CL) dark field illuminationpatter 440 that, in this embodiment, is within a range DD of 0-1.25inch. Note that the angle A of the tip (approximately 45 degrees in thisexample) determines the general angular range of light exiting the tip.There tends to be a spread of angles, in fact, and the prevailing angleof light may vary somewhat from the angle of the tip. The angle A of thetip may be altered to generate the best angle and spread for light basedupon the material used for the light pipe and it's wall thickness.

As also shown in FIG. 4 an extended bright field range DB oD-4 inchesextends beyond the dark field range. In one embodiment, the bright fieldis not illuminated or can be illuminated by a variety of other externalsources. To this end, in an alternate embodiment, the dark field lightsource may further include an external bright field illuminator 450and/or 460. In one example, the bright field illuminator is a ring lightsource (with or without a light pipe) 450 that mayor may not be mountedon the circuit board 412 (see board extensions shown in phantom). Theradial spacing of the optional, external bright field ring is variable.It may closely abut the dark field light pipe 420, or may be spaced awayfrom this light pipe as shown. According to another alternative, abright field illuminator 460 may be provided at another externallocation or locations. Note that the term “external” as used hereinshould be taken broadly to include a location that is inside the lumenof the dark field light pipe, such as, for example at the base of thepipe (adjacent to the circuit board, for example). This illuminator canbe provided as the only bright field illuminator, or in addition to thebright field ring 450.

In order to enhance the abilities of the dark field illuminator, thecontroller (see controller 370 in FIG. 3) interconnects with a number ofsegments of the LED ring. Referring again to FIG. 3, the depicted outerLED ring 336 has four exemplary segments that represent the quadrants380, 382, 384 and 386 of the overall circumference. In this example, thecontroller 370 individually addresses each of the quadrants 380-386. Inthis manner, the quadrants can be separately controlled/modulated. Theycan be turned on or off, or dimmed and brightened selectively to providethe best dark field illumination pattern for a particular subject. Ithas been observed that illumination of metallic and similar materials isoften more effective when oriented along the grain of the material. Withthe ability to dim or deactivate illumination across the grain, asignificantly improved image is attained.

In one embodiment, the scanning application or another image processorcan be used to determine the best lighting based upon the detectedimage's characteristics. This can entail a rapid cycling of lightsegments through a variety of preset on/off combinations until the bestimage quality is attained. This involves a feedback between the sensor,the scanning application and the LED controller. In other words, thesensor signal is processed by the scanning application for eachdifferent setting of the LEDs, and when an acceptable and/or optimalimage is attained, that particular setting is chosen. Image optimizationcan be based upon recognition of known fiducials or detection of maximumcontrast over a sufficiently wide portion of the viewed area ofinterest.

In a fixed-camera arrangement, this adjustment process can be carriedout once, and the selected setting can be applied to each successiveacquired image. Alternatively, in certain handheld scanningapplications, where angles and orientations of the appliance relative tothe item are likely to change, the adjustments can be made dynamicallyfor each scan. Note that a fixed setting can also be chosen where thescan will always be taken from approximately the same location. Thus, itis contemplated that any of the dark field illuminators, including thatshown in FIG. 4, can include a ring illuminator enabling selectablecontrol, with an associated LED controller. It is also expresslycontemplated that the control of LEDs can be implemented in a variety ofways and with a wide range of ring segmentation options. While foursegments are shown in the embodiment of FIG. 3, it is contemplated, inalternate embodiments, that the ring may be divided into just twohalves, or any larger number of segments can be employed. In fact, eachLED may be separately controllable/addressable in one embodiment toattain the desired dark field illumination pattern.

As shown generally in the embodiment of in FIG. 3, the light pipe caninclude at least two nested (coaxial) light pipes for providing bothdark field and bright field illumination in a single unit. The choice ofwhether dark field or bright field illumination best suits a particularsubject can be made by the controller, image processor (automated) or bythe operator (manual). According to an automated process, both brightfield and dark field illumination can be attempted, and that whichattains the best image quality is employed.

With reference now to FIG. 5, a light pipe having only a bright fieldilluminator is shown. A circuit board, 510, carries LEDs 512 surroundinga sensor 514 with associated optics 516 and a window 518 to protectthem. A light pipe 520 communicates optically with the ring illuminatorLEDs 512. The tip 522 of the light pipe 520 can be rounded or flat andcan include a diffusing (frosted, for example) surface texture forenhanced scatter of bright field light. Note that other bright fieldlight pipes described herein can have similar tip constructions andsurfaces. The walls (inner and outer) of the light pipe 522 can becoated with an opaque, non-transmissive material or can remaintransmissive. Surrounding the outer circumference of the light pipe 520at various points are each of a set of individual directing rods/lenses530 (shown in partial cross-section for clarity of rod-like structure)that each optically communicate with individual or clusters of LEDs 532.Because the field of view of the sensor is limited, and the subject mustremain within the field of view to be properly read, the LEDs 532project aiming points, typically of a different, noticeable color ontothe item of interest. For example the aiming LEDs can project aprominent blue, red or green dot while the overall illumination is awhitish light. Note that the aiming point rods herein are circular incross section. However, they may be triangular, square or any othershape that adequately denotes an aiming point.

Two exemplary illumination patterns obtained with the bright fieldilluminator of FIG. 5 are shown, respectively in FIGS. 6 and 7. In FIG.6, the field of view of the camera sensor, shown as a dashed line 602,is rectangular, while the circular bright field illuminator projects acircular illumination pattern 604. This may be desirable where thesubject has a circular outline and the corners of the field of view arenot needed, or where the symbol/subject orientation is unknown. Thescanning application and/or image acquisition circuitry can be set toreject data within these corners to speed processing. To ensure that theuser aligns the illuminator properly with respect to the subject, fouraiming dots 610 are provided around the perimeter of the illuminationfield 604. These aiming dots give instant feedback to the user so thathe or she properly aims the illumination and field of view of theappliance onto the subject. Similarly, as shown in FIG. 7, where asquare light pipe is employed, a square illumination pattern 710 isprovided. This falls within the relative field of view 602. Again,aiming dots 712 are used to ensure proper direction of the appliance bythe user. In this embodiment, the dark field illumination range DB1spans generally between approximately 0 and 12 inches from the tip 522of the light pipe. Other ranges are contemplated, of course.

FIG. 8 shows, in further detail, a nested light pipe arrangement inaccordance with an illustrative embodiment of this invention. An innerring of LEDs 802 and an outer ring of LEDs 804 are mounted on a circuitboard 806 that also includes a sensor 810. Associated optics for thesensor 812 are provided within a window area 814. As noted above, theouter light pipe 820 includes a tip 822 that is angled so as to produce,through an opening, thickness T an internally reflected beam of darkfield illumination with a span DD2 having a range of 0-1.25 inch in oneembodiment. The walls of the light pipe 820 are coated with anon-transmissive, opaque coating and the LEDs 804 of the ring are sealedby baffles 830 that isolate this illumination source with respect to theinner LEDs 802 and associated inner bright field light pipe 840. Thebright field light pipe is nested within the dark field light pipe 820and its tips 842 are recessed so as not to interfere with the openingthickness T. The tips 842 can be rounded, angled or flat. They producean appropriate bright field illumination pattern that, in thisembodiment, can extend a distance DB2 from 0-6 inches with respect tothe tip 822 of the dark field illuminator. In this manner, a brightfield subject can be contacted by the appliance and still adequatelyilluminated. Though, for contact viewing of a subject, the innerdiameter of the lumen formed by the light pipe assembly must be at leastas large in diameter as the subject being viewed. Nevertheless, incertain embodiments, it is contemplated that it is smaller and that thescanning application can include mechanisms for assembling portions ofan image formed as the appliance is moved around the image to take inall aspects of it when it is larger than the maximum field of viewafforded to the sensor. Again, as noted above, the controller candetermine either automatically or manually, whether to activate the darkfield illumination ring LEDs 804 or the bright field illumination ringLEDs 802 depending upon the subject and/or image quality obtained. A setof perimeter LEDs 850 communicate with lenses 852 in the form of rodsthat provide aiming dots as described above.

As also described generally above, the light pipe can be used torestrict the native field of view of the sensor. FIG. 9 shows a scanningappliance 902 having a rectangular cross-section light pipe 904. Thislight pipe can either be a dark field or bright field (or combination)illuminator. In this example, an item 910 includes a long, narrowsubject 912, namely a one-dimensional bar code. The illuminator projectsa pattern similar in size and shape to the bar code itself. In thismanner, when the user directs the illumination field to the item 910, heor she is naturally prompted to align the rectangular illuminationpattern with the bar code. That is, the user receives immediate feedbackas to the location of the reduced field of view, which appears as abright area that generally conforms to the subject outline. The subjectis better delineated by the reduced area, and any information outsidethis area can be omitted from the acquisition data stream, thus speedingimage processing.

With reference to FIG. 10, the overall field of view of the camera,shown as dashed line 1002, is a large square while the illumination areais a substantially narrower rectangle 1004. Again, this rectangleconforms to the shape of a one-dimensional bar code in this example. Avariety of other shapes and sizes can be provided for a selectiveillumination area with respect to the overall field of view. Smallcircles, ovals, squares and complex geometric patterns are allcontemplated. Appropriately shaped light pipes are constructed toconform to these shapes. Likewise, these light pipes can include darkfield, bright field or a combination of bright and dark field structuresas described above. Similarly, the narrowed-field of view (or “reducedfield of view”) illuminator can include aiming dots to further assistalignment on the subject.

Finally, as shown in FIG. 11, in the example of a bright fieldilluminator, a ring of LEDs 1102 is mounted on a circuit board 1104,which also includes a sensor 1106. The board is interconnected with acontroller or image acquisition device that includes scanning softwareapplications. A bright field illumination pattern extends a distance DB3from the tip of the light pipe 1120. In this example the distance DB3 isapproximately 12 inches. However other distances are expresslycontemplated. The scanning software application is adapted to rejectpixels outside of the desired field of view either through knowledge ofpixel addresses that fall outside of the desired field or because thesepixels are not appropriately illuminated and are therefore rejected(e.g., they are too dark). An appropriate optics 1110 and window 1112 isalso provided as well as a light pipe 1120 that is shaped as anelongated rectangle.

The foregoing has been a detailed description of illustrativeembodiments of this invention. Various modifications and additions canbe made without departing from the spirit and scope thereof. Forexample, it is expressly contemplated that any of the features describedin any of the above embodiments can be combined with other features toproduce the desired light pipe arrangement. Likewise, a wide variety ofdata processing devices, scanning application programs and/or hardwaresystems can be incorporated to control illumination and acquire images.Finally, the light pipes described herein can be provided with integralilluminators on a circuit board that also includes a sensor and controlfunctions that allow the sensor to communicate with the illuminator.Alternatively, the illuminator, light pipe and camera can all beseparate components that are interconnected via one or more controllers,or all connected to a common computer or processor through appropriateinterfaces. Various combinations of sensor, optics, illuminator andlight pipes are all expressly contemplated. For example, sensors may beprovided on the same circuit board as the processor and the lightsources, or any/all of these components can be separate. Appropriateinterfaces and attachment mechanisms, that should be clear to those ofordinary skill, can be provided to facilitate interaction between thevarious components described herein. In addition, while the bright fieldlight pipe is described as nested within the dark field light pipe, itis expressly contemplated that these two pipes can be reversed bypositioning the bright field illuminator outside the dark field lightpipe. Likewise, either light pipe (or light source therefor) may bedefined as a broken ring, with non-illuminated segments along theirperimeters. Accordingly, this description is meant to be taken only byway of example and not to otherwise limit the scope of the invention.

1. An image acquisition system including an image sensor for imaging atleast a portion of a subject, the system comprising: a light pipedefining an inner lumen through which the image sensor views thesubject; a light source in alignment with a proximal portion of thelight pipe, the light source adapted to project a light into the lightpipe and through the light pipe, the light pipe including a distalportion adapted to provide a high-angle bright field illuminationpattern on the subject with a first portion of the light and to reflecta second portion of the light to provide a low-angle dark fieldillumination pattern on the subject.
 2. The image acquisition systemaccording to claim 1 wherein the light pipe and the light source areeach mounted on a handheld scanning appliance.
 3. The image acquisitionsystem according to claim 1 further comprising a set of light sourcesthat each project a beam at a predetermined point with respect to thesubject to thereby assist aiming of the image sensor at the subject. 4.The image acquisition system according to claim 1 wherein the light pipeis cylindrical.
 5. The image acquisition system according to claim 1wherein the light pipe is rectangular.
 6. The image acquisition systemaccording to claim 1 wherein the light pipe is oval.
 7. The imageacquisition system according to claim 1 wherein the light pipe defines ashape that reduces a field of view of the image sensor.
 8. The imageacquisition system according to claim 1 wherein the light pipe defines acurved shape.
 9. The image acquisition system according to claim 1wherein the light pipe defines a shape conforming to dimensions of thesubject.
 10. The image acquisition system according to claim 1 furtherincluding an electronic controller that selectively controlspredetermined portions of the light source to provide selectiveillumination to portions of the light pipe.
 11. The image acquisitionsystem according to claim 1 wherein the light pipe includes an outertube and an inner tube.
 12. The image acquisition system according toclaim 11 wherein the outer tube and the inner tube are cylindrical. 13.The image acquisition system according to claim 11 wherein the outertube and the inner tube are rectangular.
 14. The image acquisitionsystem according to claim 11 wherein the outer tube and the inner tubeare oval.
 15. The image acquisition system according to claim 11 whereinthe outer tube and inner tube are mounted on a handheld scanningappliance.
 16. The image acquisition system according to claim 11wherein the inner tube defines a shape that reduces a field of view ofthe image sensor.
 17. The image acquisition system according to claim 11wherein the inner tube defines a curved shape.
 18. The image acquisitionsystem according to claim 11 wherein the inner tube defines a shapeconforming to dimensions of a predetermined subject.
 19. The imageacquisition system according to claim 11 further comprising a set oflight sources that each project a beam at a predetermined point withrespect to the subject to thereby assist aiming of the image sensor atthe subject.